This invention relates to a method of calibrating a wafer handling system, and more particularly to a method of calibrating a wafer edge gripping end effector.
In the fabrication of microelectronic devices such as integrated circuits, an electronic substrate such as a wafer must be processed in numerous processing steps, which in some cases may include as many of several hundred processing steps. During each of the processing step, the silicon wafer must be transported in and out of specific process machines such as an etcher, a physical vapor deposition chamber, a chemical vapor deposition chamber, a wafer cassette, etc. Between the processing steps, a preprocessed wafer is stored in a storage container referred to as a wafer cassette. The wafer cassette is then stored in a container known as a pod to prevent contamination.
The wafer cassette is a device that is normally molded of a plastic material which can be used to store a large number of wafers in a horizontal position. In order to maximize the number of wafers that can be stored in a cassette, the wafers are positioned relatively close to each other. For instance, the pitch distance between the wafers is approximately 2 mm in a normal cassette. The wafers, when stored in the cassette are supported along the wafer edges by molded-in supports on the inner walls of the cassette.
In order to load a wafer into or out of a process machine or wafer cassette, a device known as a wafer transport blade, wand or end effector is typically used. An end effector is a thin piece of material that may be formed in any of a variety of shapes but preferably includes a base portion with extensions commonly known as fingers. An end effector is an attachment to a robot arm that is used to transport silicon wafers, hard drive disk, or flat-panel substrates from one location to another. The end effector can be supplied for vacuum or non-vacuum applications, and may also include wafer edge gripping clamps. An end effector can be made from ceramic materials such as alumina or silicon carbide, or typically is made from a metal such as aluminum.
As indicated earlier, the processing of the silicon wafer involves moving the wafer from a cassette to various processing locations by a robot handling system. The robot handling system includes a mechanism with degrees of freedom in at least radial, angular and vertical directions with the end effector attached to the end of a robot arm. The robot arm must be able to pick up the wafers from the cassette and then transfer them to the designated stations where the wafer undergoes a variety of process steps. The robot mechanism and its associated controller must be programed with the precise location in terms of radial, angular and vertical positions of the wafer in all cassette locations and all processing station locations. A robot mechanism controller, such a central processing unit, includes programmed data to locate and retrieve the wafer precisely from the cassette or processing station.
In a typical wafer processing layout, the locations of various process stations and the cassette stand are known, and the dimensional relationships between the wafer positions in the cassette, each process station location and the robot arm are known within macro-tolerances, for example within 0.05 inches. However, the robot arm must be controlled to move the wafers within extremely close tolerances, that is within micro-tolerances, in order to prevent damage to the robot system including the end effector, wafers, the wafer cassette or other semiconductor processing equipment.
Typically, the robot system is set up and pre-programmed with the location of the wafer positions within the cassette stand, the location of the cassette stand, and other process stations using macro-tolerances. Thereafter, the robot must be programmed or taught so that the robot arm and end effector are precisely positioned during each of the operation steps within micro-tolerances. This is typically accomplished by jogging the robot arm and end effector to each location within the wafer handling process and make adjustments to the robot mechanism and control system. A substantial amount of time and effort is associated in this trial and error technique of calibrating the robot arm. Additional problems are associated with calibrating wafer edge gripping end effectors. The operator must not only correctly position the end effector but must also properly advance a movable clamp structure such as a plunger to engage the side or edge of the wafer. If the plunger is advanced to far or with too much force, the wafer can be damaged. If the plunger is not advanced far enough, this can result in the wafer being dropped by the end effector when moved from one location to another. Once the end effector is properly located for each process handling step, the precise position is then stored in the memory of the wafer handling mechanisms controller.
Further, occasionally a piece of the processing equipment such as a wafer cassette may not be precisely positioned within specifications, or the machine components wear, settle, malfunction, or components are replaced resulting in the robot control arm not being able to move to precisely the correct position for handling the wafer. Often, such situations require the robot mechanism to be reprogrammed to accommodate the new changes and new locations. Again, the trial and error method is used to position the end effector and advance a plunger as a result of the changes in the system. This is also very time-consuming.
Thus it would be desirable to provide a method of calibrating a wafer edge gripping end effector that is accurate, reliable and substantially reduces the time for calibration. The present invention provides alternatives to and advantages over the prior art.
One embodiment of the invention includes a method for calibrating a wafer edge gripping end effector. The method includes the following acts. Providing a wafer calibration tool that is substantially disc shaped having an outer edge, and a plurality of notches formed therein, wherein each notch is defined in part by an inner edge constructed and arranged to simulate the outer edge of a semiconductor wafer to be gripped by the wafer edge gripping end effector. Providing a robot having a robot arm and a wafer edge gripping end effector connected thereto, and a controller for controlling the movement of the robot arm and the wafer edge gripping end effector. The wafer edge gripping end effector includes a main base portion and a first finger and a second finger each extending from the main base portion and wherein the first and second fingers are spaced apart from each other. Each finger has a free end. A first clamp structure is positioned on the first finger near the free end of the first finger. A second clamp structure is positioned on a second finger near the free end of the second finger. A third clamp structure is also provided. At least one of the first, second and third clamp structures is movable. An actuator for moving the movable clamp structure is provided and wherein the actuator is controlled by the controller. The controller is capable of storing data regarding the position of the robot arm, end effector, and the movable clamp structure, and the controller is capable of being turned on and off. Holding the wafer calibration tool in a stationary positioned simulating the position of the semiconductor to be picked up by the wafer edge gripping end effector. Turning off the controller, and moving the robot arm and end effector to a position wherein the first and second clamp structures each engage a respective inner edge that in part defines one of the notches in the wafer calibration tool. Advancing the movable clamp structure so that the movable clamp structure engages the inner edge that in part define one of the notches in the wafer calibration tool. Turning on the controller and storing data regarding the location of the robot arm, end effector and movable clamp structure.
In another embodiment of the invention the first clamp structure is stationary.
In another embodiment of the invention the second clamp structure is stationary.
In another embodiment of the invention the third clamp structure is movable.
In another embodiment of the invention at least one of the first, second and third clamp structures includes a clamp wall constructed and arranged to be received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention the clamp wall includes a front face for engaging the inner edge that in part defines one of the notches in the wafer calibration tool, and wherein the front face is substantially straight.
In another embodiment of the invention the clamp wall is completely received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention at least one of the first, second and third clamp structures includes a bar constructed and arranged to be received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention the bar is completely received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention the bar includes an engagement face for engaging the inner edge that in part defines one of the notches in the wafer calibration tool, and wherein the engagement face is substantially straight.
In another embodiment of the invention the wafer calibration tool is generally disc shaped, with the exception of the notches formed therein, and having an outer edge with a diameter greater than a diameter of the semiconductor wafer to be picked up by the wafer edge gripping end effector.
In another embodiment of the invention the distance from the inner edge that in part defines one of the notches in the wafer calibration tool to the center of the wafer calibration tool is approximately the same as the radius of a semiconductor wafer to be picked up by the wafer edge gripping end effector.
Another embodiment of the invention further includes a coupling connecting the robot arm to the end effector, and wherein the movable clamp extends from the coupling.
Another embodiment of the invention includes a method of calibrating a wafer edge gripping end effector including the following acts. Providing a wafer calibration tool that is substantially disc shaped having an outer edge with a plurality of notches formed therein, and wherein each notch is defined in part by an inner edge constructed and arranged to simulate the outer edge of the semiconductor wafer to be gripped by the wafer edge gripping end effector. Providing a robot having a robot arm and a wafer edge gripping end effector connected thereto, and a controller for controlling the movement of the robot arm and the wafer edge gripping end effector. The wafer edge gripping end effector including a main base portion and a first finger extending from the main base portion and the first finger having a free end. A first clamp structure is positioned on the first finger near the free end of the first finger. A second clamp structures also provided. At least one of the first and second clamp structures is movable, and an actuator is provided for moving the movable clamp structure, and the actuator being controlled by the controller. The controller being capable of storing data regarding the position of the robot arm, and effector and movable clamp structure, and the controller being capable of being turned on and off. Holding a wafer calibration tool in a stationary position simulating the position of the semiconductor wafer to be picked up by the wafer edge gripping end effector. Turning off the controller and moving the robot arm and end effector to a position wherein the first clamp structure engages the inner edge that in part defines one of the notches in the wafer calibration tool. Advancing the movable clamp structure so that the movable clamp structure engages the inner edge that in part defines one of the notches in the wafer calibration tool. Turning on the controller and storing data regarding the location of the robot arm, and effector and movable structure.
In another embodiment of the invention the first clamp structure is stationary.
In another embodiment of the invention the second clamp structure is movable.
In another embodiment of the invention at least one of the first and second clamp structures includes a clamp wall constructed and arranged to be received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention the clamp wall includes a front face for engaging the inner edge that in part defines one of the notches in the calibration tool, and wherein the front face is substantially straight.
In another embodiment of the invention the clamp wall is completely received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention at least one of the first and second clamp structures includes a bar constructed and arranged to be received in one of the notches formed in the wafer calibration tool.
In another embodiment of the invention the bar is completely received in one of the notches formed in calibration tool.
In another embodiment of the invention the bar includes an engagement face for engaging the inner edge that in part defines one of the notches in the wafer calibration tool, and wherein the engagement face is substantially straight.
In another embodiment of the invention the wafer calibration tool is generally disc shaped, with the exception of the notches formed therein, and having an outer edge with a diameter greater than a diameter of the semiconductor wafer to be picked up by the wafer edge gripping end effector.
In another embodiment of the invention the distance from the inner edge that in part defines one of the notches in the wafer calibration tool to the center of the wafer calibration tool is approximately the same as a radius of the semiconductor wafer to be picked up by the wafer edge gripping end effector.
Another embodiment of the invention further includes a coupling connecting the robot arm to the end effector, and wherein the movable clamp structure extends from the coupling.
These and other objects, features and advantages of the present invention will become apparent from the following brief description of the drawings, detailed description of the preferred embodiments, and appended claims and drawings.